L14 - Puberty Flashcards
(20 cards)
Gonadotrophin Releasing Hormone (GnRH) (production, aa, secretion what trophies and M/F variation)
Hypothalamus > APG (gonadotrophs) > gonads – gametes and sex steroids
10 amino acids
Secreted in pulses
Gonadotrophins
o Luteinising Hormone (LH) – slow pulse
o Follicle Stimulating Hormone (FSH) – fast pulse
Levels in females vary due to mentration but constant in males
Prepuberty (dampening, low GnRH = ?, feedback, measurement)
- Damped down by CNS inhibitory centre (pulse generators in hypothalamus)
- Low GnRH = low LH/FSH – feedback is very sensitive
- Possible negative feedback from steroid hormones
- Measure = extremely low = small pulses and extra sensitive assays needed
Initiation (rise in?, feedback, pulsatile)
Rise in GnRH – hormones rise
Feedback decrease in sensitivity
Pulsatile sleep associated surges in GnRH begin to occur
Adrenarche (gland contribution, hormones, conversion, responsible for?, trigger)
Contribution of the adrenal gland to puberty
Androstenedione &; DHEA
Converted to testosterone & DHT in peripheral tissues
Responsible for:
Pubic & axillary hair growth
Axillary sebaceous glands
trigger?
o End of childhood independent of ACTH and cortisol
o Not essential for puberty though (e.g. adisons disease)
Puberty in boys (ages and first signs 3 and control)
- North America & Europe – between 9-14 years
- Growth of testes usually first sign
• Increasing mass of seminiferous tubules
o Controlled by testosterone
• Pubic hair development
o Controlled by testosterone
Assessed using descriptive system devised by Tanner (Boys) 5
- No pubic hair; testes < 2.5cm
- Hair at base of penis; testes > 2.5cm
- Hair spread & coarser; testes & penis growth
- More hair but no spread to thighs; further enlargement of testes & penis
- Adult appearance achieved
Other secondary sexual characteristics (6 (stimulated by what and what is spermarche)
Increased laryngeal size
Deepening of the voice
Increased bone mass
Increased mass & strength of skeletal muscle
Thickened skin
Increased & thickened hair on trunk, axillae & face= (last characteristic to appear – fully mature at ≈ age 25)
Stimulated by testosterone
Spermarche represents the age at first ejaculation as nocturnal emissions and sperm in the urine
Puberty in girls (ages and first signs 2, what its controlled by )
North America & Europe – between 8-10 years
Breast development usually first sign (Thelarche)
o Controlled by estrogen
o Maybe asymmetrical
Pubic hair development
o Controlled by testosterone
Assessed using descriptive system devised by Tanner (breasts) 5
- Preadolescent
- Breast bud
- Enlargement of breast & areola
- Protruding 2º mound of areola
- Adult size; recession of areola
Assessed using descriptive system devised by Tanner (pubes - females)
- No hair (prepubertal)
- Sparse
- Darker, coarser & spread
- Adult type but not on thighs
- Spread to thighs
Other secondary sexual characteristics: girls(4) what its stimulated by and age of menarche)
keratization of vaginal mucosa
Enlargement of labia minor and major
Uterine enlargement
Increased fat deposition in hips & thighs
o Stimulated by estrogen
o Menarche – average age is 12.8 ± 1.2 (SD) years in Caucasian girls/6 months earlier in African American - initially some cycles are anovulatory
Pubertal growth spurt (hormones cause secret of?, results in rise of? effect on epiphyseal plate, girls to boys
Androgens & oestrogen’s increase GH secretion
Pulsatile secretion of GH increases; IGF-I levels rise
Sex steroids also affect epiphyseal plate - Leg length + truck growth contribute to length
2 years earlier in girls = Girls have slower rate of growth during spurt
Bone age (establish what, steroids cause,
o Useful way of establishing physiological development
o Sex steroids cause epiphyseal closure – x ray to see to closure or not
o local (?) E production > loss of cells from reserve zone
Timing of puberty
5 boys all aged 14 – marked differences in maturation at same chronological age
Age of firms menarche (first period)
Decreased by 2-3 months / decade between 1840 & 1970
In developed countries – decrease has ceased over last 30 years
• Not many changes in socio
economic in recent times
Role of nutrition in initiation of puberty
Puberty is later in countries with “sub-optimal” socioeconomic status
Delayed puberty occurs in association with: Malnutrition and elite athletes
Moderate obesity is associated with advanced puberty
Critical weight?
Leptin – product of ob gene; expressed in adipose tissue
o Levels increase at start of puberty
o K/o mice have low Gn levels & underdeveloped gonads
o Similar phenotype in humans with mutations in leptin or receptor
o Abnormalities reversed by leptin therapy
o BUT leptin receptor is not expressed by GnRH neurones
Role of kisspeptin in initiation of puberty
Produced by CNS and Periphery
NT - Acts at a GPCR – GPR54
GPR54 is expressed by GnRH neurones
activation of GPR54 stimulates GnRH release (mutations go GPR54 = delayed puberty)
Leptin receptor expressed by Kiss1 neurones
Kisspeptin may provide link between nutritional status and fertility?
Abnormalities in pubertal timing (too late)
Psychosocial compications – can treat with testosterone to enter punerty but otherwise will go in later
o Constitutional
o gonadotrophin deficiency (low/absent central drive) - tumour
o Gonadal failure (enhanced central drive) – central drive – chemotherapy/radiation
Abnormalities in pubertal timing (too early)
Too early - precocious puberty (Appearance of secondary characteristics 2SD below avg.)
o Premature activation of HPG axis
o Excess gonadal activity
o Enhanced growth velocity
• Treatment: antagonist to dampen down axis
